A diesel oxidation catalyst (DOC) may readily oxidize NO to NO2 for treatment at an SCR or to promote regeneration of a particulate filter. One or more platinum group metals (e.g., Pt, Pd, Rh, etc.) are coupled to a substrate of the DOC and promote formation of NO2 while affording the added characteristic of low light-off temperatures. However, DOCs comprising high amounts of platinum group metals may experience degradation following a threshold number of miles of vehicle operation, thereby limiting its NO2 production capabilities.
Other attempts to address NO2 generation include DOCs with a composition including a combination of one or more platinum group metals with one or more base metal oxides. One example approach is shown by Cooper et al. in U.S. Pat. No. 4,902,487. Therein, a precious metal (e.g., a platinum group metal), such as platinum, is coated onto a ceramic honeycomb substrate. The catalyst is configured to catalyze NO into NO2 in the presence of O2. A particulate filter comprising one or more of a base metal oxides and/or La/Cs/V2O5 is located downstream of the catalyst. As such, the particulate filter may achieve lower regeneration temperatures in the presence of NO2 generated by the catalyst.
However, the inventors herein have recognized potential issues with such systems. As one example, NO2 generating catalyst may be bypassed if sulfate formation becomes an issue. Regeneration opportunities for the particulate filter using NO2 are reduced as a result.
In one example, the issues described above may be addressed by a method for generating NO2 in a catalyst comprising a washcoat with zirconium, one or more base metal oxides, and a precious metal such as palladium that does not oxidize sulfur, with an exhaust gas flow being between lower and upper threshold flow rates, and facilitating a regeneration of a particulate filter located downstream of the catalyst via NO2 when an exhaust gas temperature is greater than a threshold temperature. In this way, a NO2 production rate is calculated based on values stored in a look-up table corresponding to the exhaust gas flow rate and an exhaust gas temperature to determine if a particulate filter regeneration may be facilitated by NO2.
As one example, the particulate filter may be actively or passively regenerated. If the particulate filter is above a threshold oxygen facilitated regeneration temperature, then the filter is sufficiently hot to regenerate (e.g., burn off stored particulates) in the presence of oxygen. However, the threshold oxygen facilitated regeneration temperature is relatively high (e.g., 450-700° C.) compared to a threshold NO2 facilitated regeneration temperature (e.g., 300-450° C.). The threshold NO2 facilitated regeneration temperature corresponds to a regeneration in the presence of an amount of NO2 greater than a threshold NO2 particulate filter regeneration amount. The aftertreatment device production of NO2 is based on at least an exhaust gas flow rate. If the sensed exhaust gas flow rate is greater than a lower threshold flow rate, then NO2 produced from the aftertreatment device may promote regeneration at the particulate filter. In this way, lower exhaust gas temperatures, which may correspond to low- to mid-load driving, may be utilized to regenerate the particulate filter in conjunction with NO2 production from the aftertreatment device configured to maintain its reactivity and durability in a diesel exhaust gas environment.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.